/***
 * ASM: a very small and fast Java bytecode manipulation framework Copyright (c) 2000-2011 INRIA,
 * France Telecom All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met: 1. Redistributions of source code must retain the
 * above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions
 * in binary form must reproduce the above copyright notice, this list of conditions and the
 * following disclaimer in the documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of its contributors may be used to
 * endorse or promote products derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
 * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.googlecode.aviator.asm;

/**
 * A non standard class, field, method or code attribute.
 *
 * @author Eric Bruneton
 * @author Eugene Kuleshov
 */
public class Attribute {

  /**
   * The type of this attribute.
   */
  public final String type;

  /**
   * The raw value of this attribute, used only for unknown attributes.
   */
  byte[] value;

  /**
   * The next attribute in this attribute list. May be <tt>null</tt>.
   */
  Attribute next;

  /**
   * Constructs a new empty attribute.
   *
   * @param type the type of the attribute.
   */
  protected Attribute(final String type) {
    this.type = type;
  }

  /**
   * Returns <tt>true</tt> if this type of attribute is unknown. The default implementation of this
   * method always returns <tt>true</tt>.
   *
   * @return <tt>true</tt> if this type of attribute is unknown.
   */
  public boolean isUnknown() {
    return true;
  }

  /**
   * Returns <tt>true</tt> if this type of attribute is a code attribute.
   *
   * @return <tt>true</tt> if this type of attribute is a code attribute.
   */
  public boolean isCodeAttribute() {
    return false;
  }

  /**
   * Returns the labels corresponding to this attribute.
   *
   * @return the labels corresponding to this attribute, or <tt>null</tt> if this attribute is not a
   *         code attribute that contains labels.
   */
  protected Label[] getLabels() {
    return null;
  }

  /**
   * Reads a {@link #type type} attribute. This method must return a <i>new</i> {@link Attribute}
   * object, of type {@link #type type}, corresponding to the <tt>len</tt> bytes starting at the
   * given offset, in the given class reader.
   *
   * @param cr the class that contains the attribute to be read.
   * @param off index of the first byte of the attribute's content in {@link ClassReader#b cr.b}.
   *        The 6 attribute header bytes, containing the type and the length of the attribute, are
   *        not taken into account here.
   * @param len the length of the attribute's content.
   * @param buf buffer to be used to call {@link ClassReader#readUTF8 readUTF8},
   *        {@link ClassReader#readClass(int,char[]) readClass} or {@link ClassReader#readConst
   *        readConst}.
   * @param codeOff index of the first byte of code's attribute content in {@link ClassReader#b
   *        cr.b}, or -1 if the attribute to be read is not a code attribute. The 6 attribute header
   *        bytes, containing the type and the length of the attribute, are not taken into account
   *        here.
   * @param labels the labels of the method's code, or <tt>null</tt> if the attribute to be read is
   *        not a code attribute.
   * @return a <i>new</i> {@link Attribute} object corresponding to the given bytes.
   */
  protected Attribute read(final ClassReader cr, final int off, final int len, final char[] buf,
      final int codeOff, final Label[] labels) {
    Attribute attr = new Attribute(type);
    attr.value = new byte[len];
    System.arraycopy(cr.b, off, attr.value, 0, len);
    return attr;
  }

  /**
   * Returns the byte array form of this attribute.
   *
   * @param cw the class to which this attribute must be added. This parameter can be used to add to
   *        the constant pool of this class the items that corresponds to this attribute.
   * @param code the bytecode of the method corresponding to this code attribute, or <tt>null</tt>
   *        if this attribute is not a code attributes.
   * @param len the length of the bytecode of the method corresponding to this code attribute, or
   *        <tt>null</tt> if this attribute is not a code attribute.
   * @param maxStack the maximum stack size of the method corresponding to this code attribute, or
   *        -1 if this attribute is not a code attribute.
   * @param maxLocals the maximum number of local variables of the method corresponding to this code
   *        attribute, or -1 if this attribute is not a code attribute.
   * @return the byte array form of this attribute.
   */
  protected ByteVector write(final ClassWriter cw, final byte[] code, final int len,
      final int maxStack, final int maxLocals) {
    ByteVector v = new ByteVector();
    v.data = value;
    v.length = value.length;
    return v;
  }

  /**
   * Returns the length of the attribute list that begins with this attribute.
   *
   * @return the length of the attribute list that begins with this attribute.
   */
  final int getCount() {
    int count = 0;
    Attribute attr = this;
    while (attr != null) {
      count += 1;
      attr = attr.next;
    }
    return count;
  }

  /**
   * Returns the size of all the attributes in this attribute list.
   *
   * @param cw the class writer to be used to convert the attributes into byte arrays, with the
   *        {@link #write write} method.
   * @param code the bytecode of the method corresponding to these code attributes, or <tt>null</tt>
   *        if these attributes are not code attributes.
   * @param len the length of the bytecode of the method corresponding to these code attributes, or
   *        <tt>null</tt> if these attributes are not code attributes.
   * @param maxStack the maximum stack size of the method corresponding to these code attributes, or
   *        -1 if these attributes are not code attributes.
   * @param maxLocals the maximum number of local variables of the method corresponding to these
   *        code attributes, or -1 if these attributes are not code attributes.
   * @return the size of all the attributes in this attribute list. This size includes the size of
   *         the attribute headers.
   */
  final int getSize(final ClassWriter cw, final byte[] code, final int len, final int maxStack,
      final int maxLocals) {
    Attribute attr = this;
    int size = 0;
    while (attr != null) {
      cw.newUTF8(attr.type);
      size += attr.write(cw, code, len, maxStack, maxLocals).length + 6;
      attr = attr.next;
    }
    return size;
  }

  /**
   * Writes all the attributes of this attribute list in the given byte vector.
   *
   * @param cw the class writer to be used to convert the attributes into byte arrays, with the
   *        {@link #write write} method.
   * @param code the bytecode of the method corresponding to these code attributes, or <tt>null</tt>
   *        if these attributes are not code attributes.
   * @param len the length of the bytecode of the method corresponding to these code attributes, or
   *        <tt>null</tt> if these attributes are not code attributes.
   * @param maxStack the maximum stack size of the method corresponding to these code attributes, or
   *        -1 if these attributes are not code attributes.
   * @param maxLocals the maximum number of local variables of the method corresponding to these
   *        code attributes, or -1 if these attributes are not code attributes.
   * @param out where the attributes must be written.
   */
  final void put(final ClassWriter cw, final byte[] code, final int len, final int maxStack,
      final int maxLocals, final ByteVector out) {
    Attribute attr = this;
    while (attr != null) {
      ByteVector b = attr.write(cw, code, len, maxStack, maxLocals);
      out.putShort(cw.newUTF8(attr.type)).putInt(b.length);
      out.putByteArray(b.data, 0, b.length);
      attr = attr.next;
    }
  }
}
